purification of radioactive probe

Jose de las Heras via methods%40net.bio.net (by josenet from tiscali.co.uk)
Mon Aug 27 14:21:12 EST 2007

"Simone Marker" <marker from rhrk.uni-kl.de> wrote in message 
news:faui8f$ltc$1 from news.uni-kl.de...
> Hi,
> does anyone know if it is really necessary to purify a radioactive DNA 
> probe after labelling it by random priming? I want to use it on a northern 
> blot. So far, I worked with DIG-labelled probes, that do not need to be 
> purified after labelling. They are used directly in the hybridisation 
> solution. Is it different with radioactive probes? Do you think that 
> precipitation by salt and alcohol is sufficient for purification?
> Thank you very much,
> Simone

I *never* purify my probes (southern or northern). I label, and mix directly 
with the hyb solution. It's not inconceivable that you may get a slightly 
higher background, as some people claim, but I haven't noticed background 
problems in many years, so I'm sticking with no-purification. Of course, if 
you want to check that your labelling reaction worked, you still need to 
purify it (or check a spot with TCA), but having a bad labelling reaction by 
random priming is such a rare event, that I don't bother checking either.


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